#include <bits/stdc++.h>
using namespace std;
//template <class T> int size(const T &x) { return x.size(); }
#define rep(i,a,b) for (auto i=(a); i<(b); ++i)
#define iter(it,c) for (auto it = (c).begin(); it != (c).end(); ++it)
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef long long ll;
const int INF = 2147483647;

int main() {
    int n;
    cin >> n;
    ll ans = 0,
       starts = 0,
       cnt = 0,
       mod = 1000000007;
    rep(i,0,n) {
        int x;
        cin >> x;
        if (x == 1) {
            cnt++;
            cnt %= mod;
            starts++;
        } else if (x == 2) {
            cnt *= 2;
            cnt %= mod;
        } else {
            ans += cnt;
            ans %= mod;
            ans += mod - starts;
            ans %= mod;
        }
    }
    cout << ans << endl;

    return 0;
}